Chunli Dai oral presentation (SN1-Fri2-2-2)
Applications of TOF-SIMS on Passive Film Analysis of High Nitrogen Stainless Steels
Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, 110016 Shenyang, China
Passive film on stainless steels plays a decisive role in corrosion resistance. With thickness of several nanometers and with complex structure and composition, it is hard to be fully characterized with commonly used surface analytics like AES or XPS. TOF-SIMS owns the capability to characterize very thin passive films not only because its high resolution in both depth and mass, but also its ability to resolve the clusters ions containing nitrogen, oxygen or hydrogen.
High nitrogen stainless steels (HNS) has excellent comprehensive properties of strength, ductility, corrosion resistance as well as biocompatibility. More than 0.4 wt% of nitrogen was used to replace nickel to stabilize austenitic microstructure. It supposed that pitting corrosion resistance of HNS is more excellent than conventional stainless steels, which was generally caused by nitrogen addition. However, the underlying reason is still unclear[1, 2]. XPS is limited by the species and spatial resolution and AES cannot easily give the chemical states of element in the passive films. So Tof-SIMS depth profiling and 3D view technique were applied to investigate the passive film of HNS. The passive film of HNS was found of a trilayer structure. Compared with the passive film of conventional stainless steels, there was an additional nitrogen enrichment layer in the HNS passive film. It can be distinguished as chromium nitride by Tof-SIMS spectra analysis. The nitrogen enrichment layer also heavily doped the chromium oxide layer and reduces the oxygen vacancies. It made the passive film of the HNS more stable and more protective, which resulted in much better pitting corrosion resistance.